In the FAIR project (Facility for Antiproton and Ion Research) at the GSI Helmholtz Centre for Heavy Ion Research GmbH, high intensity heavy ion beams will be provided by the superconducting synchrotron SIS100. Medium charge state ions will be used instead of high charge state ions. The medium charge state ions on the one hand shift the space charge limit towards higher intensities and, on the other hand, avoid intensity losses in stripper stages. The most demanding challenges in the operation with medium charge state heavy ions are beam losses due to charge exchange in collisions with residual gas molecules. Further ionized ions are separated from the circulating beam and get lost on the chamber wall, while releasing a big amount of gas via ion stimulated desorption. The local pressure rise increases the probability for further charge exchange of beam ions, and a self-amplification can evolve. This process may result in a complete beam loss. One way to damp this amplification is given by the installation of ion-catchers or collimators, which ensure perpendicular loss on special low desorbing surfaces at the positions of beam loss.
The ion optical lattice of the SIS100 of the FAIR accelerator complex has been optimized for the usage of collimators. Almost 100% of the ionization losses can be caught by the ion-catcher system. In the arcs of the synchrotron, a total of 60 ion-catchers is located between the superconducting quadrupoles in a cryogenic environment. This thesis adresses the development, the construction, and the test of a cryocatcher prototype.
In SIS18, an ion-catcher system has been installed successfully. In this work it is compared to the ion-catcher system of SIS100, and different measurements with the existing system are presented. Based on the requirements for the new system, the collimator block and its support structure, as well as the surrounding cryogenic, copper plated vacuum chamber is described. The cold surface of the vacuum chamber acts as a cryopump that quickly binds desorbed gas molecules in order to keep the charge exchange losses low. During the construction, particular care was given to the minimization of the pressure on the beam axis.
In order to test the cryocatcher-prototype under realistic conditions, a dedicated test-setup with cryostat was designed, constructed, and built. This test-setup was installed at an existing beamline of the GSI-accelerator-complex. The prototype was cooled with liquid nitrogen and liquid helium and then, subsequently, irradiated with heavy ion beams. During the measurement of the ion induced pressure rise in the cold chamber, a rise of the desorption yields with rising beam energy has been observed for the very first time. Measurements at room temperature showed the known decrease of the pressure rise in the investigated energy regime. A transition temperature of 18 K, underneath where hydrogen gets adsorbed, could be verified several times. This result is crucial for a reliable operation of the SIS100.
In summary, the cryocatcher-protoype fulfills all requirements and the tests were satisfactory. A series-production for SIS100 can be launched.